netcdf 20031231_chilbolton_lwc-adiabatic-method {
dimensions:
time = 2868 ;
height = 192 ;
variables:
float time(time) ;
time:axis = "T" ;
time:units = "hours since 2003-12-31 00:00:00 +0:00" ;
time:long_name = "Time UTC" ;
time:standard_name = "time" ;
float height(height) ;
height:axis = "Z" ;
height:units = "m" ;
height:long_name = "Height above mean sea level" ;
height:standard_name = "height" ;
float latitude ;
latitude:units = "degrees_north" ;
latitude:long_name = "Latitude of site" ;
latitude:standard_name = "latitude" ;
float longitude ;
longitude:units = "degrees_east" ;
longitude:long_name = "Longitude of site" ;
longitude:standard_name = "longitude" ;
float altitude ;
altitude:units = "m" ;
altitude:long_name = "Height of radar above mean sea level" ;
float lwc(time, height) ;
lwc:long_name = "Liquid water content" ;
lwc:units = "kg m-3" ;
lwc:units_html = "kg m-3" ;
lwc:error_variable = "lwc_error" ;
lwc:missing_value = -999.f ;
lwc:_FillValue = -999.f ;
lwc:comment = "This variable was calculated for the profiles where the \"categorization\" data has diagnosed that liquid water is present \n",
"and liquid water path is available from a coincident microwave radiometer. The model temperature and pressure were used to estimate the \n",
"theoretical adiabatic liquid water content gradient for each cloud base and the adiabatic liquid water content is then scaled so that its \n",
"integral matches the radiometer measurement so that the liquid water content now follows a quasi-adiabatic profile. If the liquid layer is \n",
"detected by the lidar only, there is the potential for cloud top height to be underestimated and so if the adiabatic integrated liquid water content is \n",
"less than that measured by the \n",
"microwave radiometer, the cloud top is extended until the adiabatic integrated liquid water content agrees with the value measured by the microwave radiometer. \n",
"Missing values indicate that either liquid water was diagnosed but no microwave radiometer data was available, or that rain is present in the profile \n",
"and therefore the vertical extent of liquid layers is difficult to ascertain. " ;
lwc:plot_range = 1.e-05f, 0.01f ;
lwc:plot_scale = "logarithmic" ;
float lwc_error(time, height) ;
lwc_error:long_name = "Random error in liquid water content, one standard deviation" ;
lwc_error:units = "dB" ;
lwc_error:plot_range = 0.f, 2.f ;
lwc_error:plot_scale = "linear" ;
lwc_error:missing_value = -999.f ;
lwc_error:_FillValue = -999.f ;
lwc_error:comment = "This variable is an estimate of the random error in liquid water content due to the uncertainty in the microwave radiometer \n",
"liquid water path retrieval and the uncertainty in cloud base and/or cloud top height. This is associated with the resolution of the grid used, 60 m, \n",
"which can affect both cloud base and cloud top. If the liquid layer is detected by the lidar only, there is the potential for cloud top height to be underestimated. \n",
"Similarly, there is the possibility that the lidar may not detect the second cloud base when multiple layers are present \n",
"and the cloud base will be overestimated. It is assumed that the error contribution arising from using the model temperature and pressure at cloud base \n",
"is negligible." ;
float lwc_adiabatic(time, height) ;
lwc_adiabatic:long_name = "Adiabatic liquid water content" ;
lwc_adiabatic:units = "kg m-3" ;
lwc_adiabatic:units_html = "kg m-3" ;
lwc_adiabatic:missing_value = -999.f ;
lwc_adiabatic:_FillValue = -999.f ;
lwc_adiabatic:comment = "This variable was calculated for the profiles where the \"categorization\" data has diagnosed that liquid water is present. \n",
"The model temperature and pressure were used to estimate the theoretical adiabatic liquid water content gradient for each cloud base." ;
lwc_adiabatic:plot_range = 1.e-05f, 0.01f ;
lwc_adiabatic:plot_scale = "logarithmic" ;
byte lwc_retrieval_status(time, height) ;
lwc_retrieval_status:long_name = "Liquid water content retrieval status" ;
lwc_retrieval_status:plot_range = 0b, 6b ;
lwc_retrieval_status:comment = "This variable describes whether a retrieval was performed for each pixel, and its associated quality, in the form of 6 different classes.\n",
"The classes are defined in the definition and long_definition attributes. The most reliable retrieval is that when both radar and lidar detect the liquid layer, and microwave radiometer \n",
"data is present, indicated by the value 1. The next most reliable is when microwave radiometer data is used to adjust the cloud depth \n",
"when the radar does not detect the liquid layer, indicated by the value 2, with a value of 3 indicating the cloud pixels that have been added at cloud top to avoid the profile becoming superadiabatic.\n",
"A value of 4 indicates that microwave radiometer data were not available but the liquid layers were well defined. If cloud top was not well defined then this is indicated by a value of 5. \n",
"The full retrieval of liquid water content, which requires liquid water path from the microwave radiometer, given in the lwc variable was only performed for classes 1-3. \n",
"A retrieval of adiabatic liquid water content, which does not include any liquid water path information from the microwave radiometer, \n",
"was performed for classes 1-5 where class 1 is equivalent to class 4 and classes 2-3 correspond to class 5. \n",
"No attempt is made to retrieve liquid water content when rain is present; this is indicated by the value 6." ;
lwc_retrieval_status:definition = "0: No liquid water\n",
"1: Reliable retrieval\n",
"2: Adiabatic retrieval: cloud top adjusted\n",
"3: Adiabatic retrieval: new cloud pixel\n",
"4: Adiabatic retrieval: no lwp\n",
"5: Unreliable adiabatic retrieval\n",
"6: Rain present: no retrieval" ;
lwc_retrieval_status:long_definition = "0: No liquid water detected\n",
"1: Reliable retrieval \n",
"2: Adiabatic retrieval where cloud top has been adjusted to match liquid water path from microwave radiometer because layer is not detected by radar\n",
"3: Adiabatic retrieval: new cloud pixels where cloud top has been adjusted to match liquid water path from microwave radiometer because layer is not detected by radar\n",
"4: Adiabatic retrieval where no liquid water path is available\n",
"5: Unreliable adiabatic retrieval: liquid water detected only by the lidar and no liquid water path is available: cloud top may be higher than diagnosed cloud top since lidar signal has been attenuated\n",
"6: Rain present: cloud extent is difficult to ascertain and liquid water path also uncertain" ;
lwc_retrieval_status:legend_key_red = 1.f, 0.4f, 0.f, 0.f, 1.f, 1.f, 0.4f ;
lwc_retrieval_status:legend_key_green = 1.f, 0.8f, 0.f, 1.f, 0.6f, 0.f, 0.4f ;
lwc_retrieval_status:legend_key_blue = 1.f, 1.f, 1.f, 0.f, 0.f, 0.f, 0.4f ;
float lwp(time) ;
lwp:long_name = "Liquid water path" ;
lwp:units = "kg m-2" ;
lwp:missing_value = -999.f ;
lwp:_FillValue = -999.f ;
lwp:comment = "This variable is the vertically integrated liquid water directly over the site.\n",
"The temporal correlation of errors in liquid water path means that it is not really meaningful to distinguish bias from random error,\n",
"so only an error variable is provided.\n",
"Original comment: This variable is the vertically integrated liquid water content, or liquid water path (lwp), obtained using dual-wavelength microwave\n",
"radiometer, lidar and information from a forecast model. The lwp is assumed to be proportional to microwave optical depth, and the\n",
"coefficients used to derive it are obtained as follows. For the liquid water coefficients, the lidar is used to locate the cloud and the model to\n",
"diagnose cloud base temperature. The water vapour coefficients are derived from model temperature and vertical humidity distribution. Note that\n",
"humidity is not used in an absolute sense but only in the sense of determining the effective emission temperature of a given water vapour\n",
"path. Finally, periods of clear sky identified by lidar are used to estimate calibration errors in the radiometers using the fact that lwp\n",
"retrieved in these regions should be zero." ;
lwp:units_html = "kg m-2" ;
lwp:error_variable = "lwp_error" ;
lwp:plot_range = -100.f, 1000.f ;
lwp:plot_scale = "linear" ;
float lwp_error(time) ;
lwp_error:units = "kg m-2" ;
lwp_error:long_name = "Error in liquid water path, one standard deviation" ;
lwp_error:missing_value = -999.f ;
lwp_error:_FillValue = -999.f ;
lwp_error:comment = "This variable is a rough estimate of the one-standard-deviation error in liquid water path, calculated as a\n",
"combination of a 20 g m-2 linear error and a 25% fractional error." ;
lwp_error:units_html = "kg m-2" ;
float lwc_th(time, height) ;
lwc_th:long_name = "Liquid water content (tophat distribution)" ;
lwc_th:units = "kg m-3" ;
lwc_th:units_html = "kg m-3" ;
lwc_th:missing_value = -999.f ;
lwc_th:_FillValue = -999.f ;
lwc_th:comment = "This variable is the liquid water content assuming a tophat distribution. I.e. the profile of liquid water content in each layer is constant." ;
lwc_th:plot_range = 1.e-05f, 0.01f ;
lwc_th:plot_scale = "logarithmic" ;
// global attributes:
:Conventions = "CF-1.0" ;
:title = "Liquid water content from Chilbolton" ;
:location = "Chilbolton" ;
:day = 31s ;
:month = 12s ;
:year = 2003s ;
:history = "24 Aug 2006 16:52:58 - Generated from categorization data by Ewan O\'Connor \n",
"Categorization history: 06 Oct 2004 19:20:49 - Generated from level 1 data by Ewan O\'Connor \n",
"Radar history: Wed Feb 25 02:03:05 2004 - NetCDF generated from original data by Nicolas Gaussiat on hogwarts\n",
"Wed May 12 10:20:06 2004 - Recalibrated (-3.3 dB) by Nicolas Gaussiat on hogwarts\n",
"Wed May 12 11:41:41 2004 - Inserted incoherent reflectivity factor by radar on hogwarts\n",
"(Incoherent processing history: Wed Feb 25 01:18:35 2004 - NetCDF generated from original data by Nicolas Gaussiat on hogwarts\n",
"Wed May 12 10:36:33 2004 - Recalibrated (+2 dB) by Nicolas Gaussiat on hogwarts)\n",
"Lidar history: Tue Aug 17 17:31:43 2004 - NetCDF generated from original data by Ewan O\'Connor on hogwarts\n",
"Model history: Fri Sep 24 14:15:07 BST 2004 - NetCDF generated from original data by Ewan O\'Connor using cnmodel2nc on hogwarts\n",
"Gauge history: Recorded using Microlink 3000 series DAQ\n",
"2004-01-08 15:19:01 : converted to netCDF from FORMAT5 using Matlab 6.5.0.180913a (R13) running on GLNX86\n",
"Microwave radiometer history: Recorded using Microlink 3000 series DAQ\n",
"2004-01-08 14:41:25 : converted to netCDF from FORMAT5 using Matlab 6.5.0.180913a (R13) running on GLNX86\n",
"2004-09-28 16:46:46 : Liquid and vapour vater path produced by Nicolas Gaussiat on hagrid\n",
"" ;
:source = "CloudNet categorization product (software version 0.9) comprising:\n",
"Chilbolton 94-GHz Cloud Radar (Galileo)\n",
"Frequency: 94.00 GHz\n",
"Antenna diameter: 0.46 m\n",
"Axis separation of transmit and receive antennas: 0.66 m\n",
"Peak power: 1.6 kW\n",
"Pulse width: 0.5 us\n",
"Pulse repetition frequency: 6250 Hz\n",
"Beam width: 0.5 degrees;\n",
"Chilbolton Vaisala 905-nm CT75K lidar ceilometer\n",
"Wavelength: 905 nm\n",
"Half-angle beam divergence: 0.75 mrad\n",
"Half-angle field of view: 0.66 mrad;\n",
"UK Met Office Unified Model (Mesoscale);\n",
"meteorological sensors;\n",
"Microwave radiometers" ;
:institution = "Data processed at the Department of Meteorology, University of Reading." ;
:comment = "This dataset contains liquid water content calculated by using radar and lidar to identify the liquid cloud base and top in each profile, \n",
"using the model temperature and pressure to calculate the adiabatic liquid water content in each cloud layer, and then using dual-wavelength \n",
"microwave radiometers to scale the liquid water content values to yield the correct liquid water path. While this simple partitioning with \n",
"height is somewhat uncertain, liquid water clouds are frequently thin, occupying only a few vertical model levels, so this dataset is adequate \n",
"for testing liquid water content in models. Also available for comparison is the adiabatic liquid water content (i.e. unscaled by the microwave radiometer liquid water path)." ;
}